MX2014002086A - Process to obtain mixtures of imidazolines and corrosion inhibitors from coffee waste. - Google Patents

Abstract

The biphasic extraction from coffee waste without a prior drying process, to obtain coffee oil, which is transesterified with KOH catalyzed methanol to produce mixtures of glycerol free methylic esters, also known as coffee oil biodiesel, which is subjected to an aminolysis reaction with aminoethylethanolamine (AEEA) by heating to 140-160 DEG C. at atmospheric pressure with a subsequent dehydration reaction at the same temperature but at a reduced pressure of 200 to 300 mmHg, in order to achieve cyclization of the intermediary amides into the corresponding imidazolines. Alternatively process, coffee oil can be submitted to the same aminolysis procedure with aminoethylethanolamine (AEEA) at 140 to 160 DEG C. and atmospheric pressure with a subsequent dehydration reaction at the same temperature but at a reduced pressure of 200 to 300 mmHg, to produce imidazolines that contain the residual glycerol of the original triglycerides. The imidazolines mixtures obtained by any of the two alter native processes present a high performance as corrosion inhibitors. The imidazolines mixtures obtained according to the present invention are characterized in that they contain a high grade of unsaturation in the alkyl chains, which provides a higher adherence to the metallic surfaces than saturated imidazolines. This imidazoline mixture constitutes a corrosion inhibitor of high performance, low toxicity and suitable biodegradability.

Description

PROCESS FOR OBTAINING MIXES OF IMIDAZOLINES AND CORROSION INHIBITORS FROM THE WASTE OF COFFEE TECHNICAL FIELD The present invention includes innovative processes related to the extraction and processing of the oils contained in coffee waste, including its transformation into mixtures of 1-hydroxyethyl-2-alkyl substituted imidazolines and their application as inhibitors of corrosion in ducts, tanks and other industrial facilities for transportation, storage and processing of liquid and gas hydrocarbons. The incorporation of the molecular structure of the doubly unsaturated linoleic acid contained in the triglycerides of the coffee oil confers to the imidazolines reported here superior adhesion to metallic surfaces, due to the interaction of the pi electrons of the double bonds with the electrons of the metal surface. The present invention also represents a solution for decontaminating coffee wastes that are recognized as contaminants of soils and water banks due to the toxic characteristics of caffeine, through the process where the residual caffeine is removed from the coffee waste.

BACKGROUND Internal corrosion of ducts, tanks and process facilities is a serious problem that affects the safe, reliable and environmentally harmless operation of industrial processes. Most metallic materials are very vulnerable to contact with water and a variety of electrolytes. This is a particularly serious problem in the oil industry, due to the increasing salinity and the total acidity of the primary production, which impacts the entire chain of transport, refining and distribution processes.

Internal corrosion of ducts, tanks and industrial facilities caused by the transport, storage or processing of fluids containing water and electrolytes can be controlled by corrosion inhibitors. The addition of corrosion inhibitors within transported, stored or processed hydrocarbons has shown significant successes in corrosion mitigation below 2 mils per year, a parameter required in many normative documents to ensure several decades of life Useful of the metallic components (Norma NRF-005-PEMEX-2009). There is a wide variety of products that serve as inhibitors of corrosion, highlighting the family of compounds called imidazolines, which have the peculiarity of inhibiting corrosion in low doses of 5 to 150 parts per million, in addition to being among the most friendly substances with the environment. The 2-alkyl-imidazolines have been used as corrosion inhibitors since the 1940s in the petroleum industry. These inhibitors are used as mixtures of imidazolines which present in the 2-position a hydrocarbon chain of 7 to 19 carbon atoms (hydrophobic group) and in the 1-position a polar group, such as hydroxyethyl or acylaminoethyl. The imidazolines can also be quaternized to be employed as cationic surfactants, fabric softeners, hair conditioners or antistatic agents.

Imidazolines of type 2- (2-alkyl-4,5-dihydro-1 H-imidazol-1-yl) ethanol, derived from vegetable oils, such as palm or coconut oil, or from animal fats, such as tallow, They are marketed with different applications. An important use of this type of compounds is the inhibition of the corrosion of pipelines, tanks and other facilities of the industries that involve the transport, processing and storage of hydrocarbons. However, to date, the production and application of imidazolines derived from the oil extracted from the waste coffee has not been conceived. Even though the use of coffee oil to obtain biofuels is known, a process to obtain imidazolines derived from coffee oil has not been reported. The waste of Coffee resulting from the preparation of coffee beverages and other products made from coffee beans contain 13 to 15% (dry base) of oil, which includes linoleic acid as the most abundant of the fatty acids present in this oil. Linoleic acid is doubly unsaturated, which gives the imidazolines containing it a superior adhesion to metal surfaces, due to the interaction of the pi electrons of the double bonds with the electrons of the metal surface.

The imidazolines derived from coffee oil have, besides excellent qualities as corrosion inhibitors, a low toxicity and a good level of biodegradability in the environment, which makes them a very suitable and environmentally friendly option as corrosion inhibitors in the industry or as fabric softeners, antistatic hair conditioning agents, among others.

Coffee is one of the main agricultural products worldwide and gives rise to one of the highest consumption beverages. It is estimated that the world production of coffee is close to 6 million tons, with 10 leading countries. Coffee consumption is very variable, from 12 Kg per capita per year in Finland, with a general average of 1.2 Kg per capita. Depending on the variety, the oil content in coffee waste varies between 13-15% (dry basis). Most residues of ground coffee beans are disposed of in landfills, although their use has been proposed in composting. Coffee wastes are known as contaminants of soils and water banks due to the toxic characteristics of caffeine.

Coffee oil is a mixture of triglycerides consisting of fatty acids of 14 to 22 carbon atoms, with a composition of fatty acids that depends on the variety and origin of coffee. A composition has been reported percentage of 44% linoleic acid, 33% palmitic acid, 9% oleic acid, 7% stearic acid and other minor fatty acids.

Various processes have been described for the extraction of coffee oil, with a view to its transformation into biodiesel. In these processes soxhlet equipment, supercritical CO2 for dry coffee wastes and ultrasound-assisted biphasic extraction have been used.

The processes previously indicated for the extraction of coffee oil are, in our view, unviable on an industrial scale, because they require previously dried coffee and very expensive equipment at an industrial level, such as those that would allow the use of ultrasound or supercritical CO2.

In the specialized literature there are relevant references to background and advances of knowledge on which the present invention is based: Ortega-Toledo, D.M .; Gonzalez-Rodriguez, J.G .; Casales, M .; Martinez-Gomez, L. Corrosion Science, 53, 3780-3787 (2011); Radcriffe, R. US Pat 2,200,815 (1940); Mcyer, G.R., US Pat 6,448,411 (2002); Daglia, M; Racchi, M .; Papetti, A .; Lanni, C .; Govoni, S .; Gazzani, G. Journal of Agricultural and Food Chemistry, 52, 1700-1704 (2004); Barkenbus, C .; Zimmerman, A. J. Journal of the American Chemical Society 49, 2061-2064 (1927); Kondamudi, N .; Mohapatra, S.K .; Misra, M. Journal of Agricultural and Food Chemistry 56 (24), 11757-11760 (2008); Scanlan, J. US Pat 6,488,732 (2002); Martin, M. J. et al., Talanta, 54, 291-297 (2001); Misra, M .; Mohapatra, S. K .; Kondamudi, N.V. US 2010/0287823; Couto, R.M .; Fernandes, J .; Gomes da Silva, M.D.R .; Simoes, P.C. J. Supercritical Fluids, 51 (2), 159-166 (2009); Oliveira, L. S .; Franca, A. S .; Camargos, and Ferraz, V. P. Bioresource Technology 99, 3244-3250 (2008); Abdullah, M .; Bulent Koc, A. Renewable Energy 50, 965-970 (2013); Al-Hamamre, Z .; Foerster, S .; Hartmann, F .; Kroger, M .; Kaltschmitt, M. Fuel, 96, 70-76 (2012); Khan, N.A .; Brown, J.B. Journal of the American Oil Chemists' Society, 30, 606-609 (1953); Seung-H. I or, Young-Wun Kim, Kunwoo Chung, Seung-Yeop Baik, Joon-Seop Kim. Corrosion Science, 59, 42-54 (2012); Rivera-Grau, L. M .; Casales, M .; Rule I; Ortega-Toledo, D. M .; Ascencio-Gutierrez, J. A .; Gonzalez-Rodriguez, J. G .; Martinez-Gomez, L. International Journal of Electrochemical Science, 7, 12391-12403 (2012); Erik M. Quandt, Michael J. Hammerling, Ryan M. Summers, Peter B. Otoupal, Ben Slater, Razan N. Alnahhas, Aurko Dasgupta, James L. Bachman, Mani V. Subramanian, and Jeffrcy E. Barrick, ACS Synth. Biol., March 8, 2013; Williams CF, McLain JE, J Environ Qual. 2012 Sep-Oct; 41 (5): 1473-80.

Within the patents reviewed to support the novelty of the present invention is the patent JP2013013344 which presents a method for the production of coffee oil for aromatic applications in which oil is extracted from roasted and hydrated coffee beans from the oil / water emulsion by means of the centrifugation process. The aforementioned patent makes no mention of the use of linoleic acid contained in the triglycerides present in the oil extracted from coffee to obtain imidazolines, whose main characteristic is a high adhesion on metal surfaces.

The patent with registration CN 102875160 A presents an invention related to the production of additives of ceramic compounds by means of the processes of induction of microwave radiation, hydroxymethylation and esterification where the raw material used are the lignosulfonates obtained from the coffee powder . This patent does not describe any process related to the production of coffee biodiesel and imidazolines, such as the process of transesterification with methanol catalyzed with KOH and the process of aminolysis with aminoethylethanolamine (AEEA) respectively.

The patent with registration US2007 / 0259084 A1 is related to the obtaining of surfactants derived from coffee by means of reactions of transesterification of sugars and coffee oil, the purpose being the production of emulsions of this organic compound for use in the improvement of coffee products, such as instant coffee, improving the characteristics of aroma and flavor. Likewise, this patent does not contemplate the use of coffee oil, nor processes inherent to the production of imidazolines for their use as corrosion inhibitors in the hydrocarbon industry.

The patent of invention with application number AR2010P100096 20100115 presents a method for obtaining biodiesel from the use of the coffee fluff. The invention refers to the recielado of coffee residue and the production of a fuel of a renewable nature and low environmental impact, however does not refer to any method or process for the use of organic waste from coffee as a corrosion inhibitor interior presented in ducts, tanks, and other industrial facilities related to the storage and transportation of hydrocarbons.

The patent with registration US 2010/0287823 A1 describes a method for the production of biofuel using one or more sources of coffee as a raw material, such as green coffee beans, roasted coffee beans, ground coffee or ground coffee products. The biofuel is obtained from a process of transesterification of triglycerides found in the coffee sources mentioned, where the products obtained can be used for other uses such as in the manufacture of cosmetics, medicines, food products or combustible materials, without However, this patent does not consider aminolysis process with aminoethylethanolamine (AEEA) for the production of mixtures of imidazolines.

Other of the patents reviewed that contemplate the production of biofuel are the patents US8545702 and US8540881 B1, which are related to the production of biodiesel and / or glycerin from different processes such as transesterification of oils. These patents also do not consider the use of coffee residues, nor the extraction of oil from it as raw material for the preparation of corrosion inhibitors.

There are also patents related to obtaining imidazolines and their compounds derived from chemical processes for different applications, such as processing imidazolines of polycarboxylic acids for the preparation of cleaning products (patent US5049315), imidazolines (patent US2161938), process for the preparation of imidazoline substituted as fabric softener for the textile industry (US5154841). However, none of these patents gives a reference related to the processing of coffee residues and the use of linoleic acid containing the triglycerides present in the oil extracted from coffee for the synthesis of 2-Alkyl-1-hydroxyethylimidazoline, which is doubly unsaturated and whose main characteristic is a high adherence in metallic surfaces.

BRIEF DESCRIPTION OF THE INVENTION The main novelty provided by the invention is the incorporation of an additional use for ground coffee waste, by extracting the oil it contains (typically 10-15%) to be used as a raw material in the production of imidazolines with a high degree of of unsaturation.

The mixtures of imidazolines obtained by the processes described in the present invention have application, especially as corrosion inhibitors of high performance, low toxicity and good biodegradability.

Linoleic acid is the most abundant fatty acid in coffee oil and is doubly unsaturated, which confers to the imidazolines containing the hydrocarbon chains of linoleic acid an adhesion to metal surfaces superior to the adherence of imidazolines of other fatty acids, due to the interaction of the pi electrons of the double bonds with the electrons of the metal surface.

The extraction method proposed for coffee oil improves what is described in the literature, as it consists of a biphasic extraction, which does not require previously dried coffee, with the consequent energy saving of the evaporation of 550 to 650 Kg of water per ton of waste coffee.

The coffee oil is subjected to a transesterification process catalyzed with KOH, using conventional methods described for the preparation of biodiesel, and subsequently the biodiesel obtained is subjected to aminolysis process with aminoethylethanolamine (AEEA), by heating between 140 and 160 ° C and subsequent heating under reduced pressure of 200 to 300 mmHg at the same temperature until the stoichiometric amount of water is removed, to produce the mixture of imidazolines by delation of the intermediate amides produced in the aminolysis.

An alternative that shortens the process is the direct treatment of the oil obtained from coffee waste, under the same conditions described above for biodiesel. With this alternative, the imidazolines produced contain the glycerol that is generated in the aminolysis process. Glycerol, present in the imidazoline mixtures of the corrosion inhibitor formulations, does not affect the performance of the product.

Coffee wastes are known as contaminants of soils and water banks due to the toxic characteristics of caffeine. Through the process described in this patent, the defatted coffee residue improves its qualities as fertilizer or compost input, because in the Biphasic extraction process of the oil completely eliminates residual caffeine.

BRIEF DESCRIPTION OF THE FIGURES Figure 1. Representation of the chemical structure of a doubly unsaturated imidazoline and the interactions with the metal surface. The nitrogen and OH locations are marked. With segmented lines, the foreseeable interactions with the metallic surface are marked, including the electronic clouds of the interactions.

Figure 2. Flow diagram of the process of extraction and transformation of waste coffee oil into imidazolines. It includes process A of three stages and process B of two stages.

Figure 3. Diagram of the process of obtaining mixtures of imidazolines from coffee oil.

Figure 4 A. Testing of the mixture of imidazolines as a corrosion inhibitor at a concentration of 5 ppm.

Figure 4 B. Test of the mixture of imidazolines as a corrosion inhibitor at a concentration of 10 ppm.

Figure 4 C. Test of the mixture of imidazolines as a corrosion inhibitor at a concentration of 25 ppm.

Figure 4 D. Test of the mixture of imidazolines as a corrosion inhibitor at a concentration of 50 ppm.

Figure 4 E. Test of the mixture of imidazolines as a corrosion inhibitor at a concentration of 100 ppm.

DETAILED DESCRIPTION OF THE INVENTION In the present invention, two processes related to the production of mixtures of imidazolines are described by processing the oil extracted from the ground coffee waste.

The structure of the main imidazolines of general formula (I) obtained from the coffee oil is presented below: Where in the 1-position of the imidazoline ring they have a 2-hydroxyethyl chain; and in the 2 (R) position, a hydrocarbon chain of the following fatty acids present in the oil obtained from the waste coffee, mainly linoleic acid (between 44 and 46%, preferably 44%), CH2 (CH2) 6CH = CHCH2CH = CH (CH2) 4CH3; palmitic acid (between 32 to 35%, preferably 34%) -CH2 (CH2) i3CH3; and other minor fatty acids, among which oleic acid (between 9 and 10%, preferably 9%), -CH2 (CH2) 6CH = CH (CH2) 7CH3; and stearic acid (between 6 and 7%, preferably 7%), -CH2 (CH2) I5CH3.

The main advantage of imidazolines derived from linoleic acid is the presence in the hydrocarbon chain with two unconjugated double bonds, which gives it a greater adherence to metal surfaces and consequently better performance as corrosion inhibitors. This is due to the better stabilization capacity of the oxide layer and the longer duration of the hydrophobic effect, which minimizes the contact of moisture with the metal surface.

The present invention includes two alternative processes for obtaining mixtures of imidazolines derived from coffee waste oil. The first of these processes, which we call process A, consists of three stages: Stage 1. The extraction of the oil present in the waste coffee, without previous drying, in a biphasic system water-methanol-heptane for batch processes or water-heptane for continuous processes, with the corresponding separation of the heptane phase and concentration to dryness at moderately reduced pressure between 100 and 200 mmHg, recovering the heptane for re-use by a simple distillation method and leaving the oil completely free of volatile components, such as water or solvents.

Stage 2. The transesterification with methanol (of extracted coffee oil), catalyzed with KOH, to obtain biodiesel, with the consequent separation of glycerol through a decanting process in a tank with a lower valve with a glass peephole.

Stage 3. The final stage consists of two consecutive reactions: the aminolysis of biodiesel with aminoethylethanolamine (AEEA), at temperatures of 140 - 160 ° C and then the delation, by heating the mixture at the same temperature, at pressures of 200 - 300 mmHg.

The second process for the production of imidazolines from the waste or coffee waste contemplated by the present invention, which we call process B, consists of two stages: Stage 1. The extraction of the oil present in the waste coffee, without previous drying, in a biphasic system water-methanol-heptane for batch processes or water-heptane for continuous processes, with the corresponding separation of the heptane phase and concentration to dryness at moderately reduced pressure, between 100 and 200 mmHg, recovering the heptane for re-use by a simple distillation method and leaving the oil completely free of volatile components, such as water or solvents.

Stage 2. The direct aminolysis of the waste coffee oil with AEEA at temperatures of 140-160 ° C and then the heating by heating the reaction mixture at the same temperature, at pressures of 200-300 mmHg.

The mixture of imidazolines obtained in accordance with process A is characterized as being free of glycerol and the mixture of imidazolines obtained in accordance with process B is characterized as containing the natural glycerol derived from the triglycerides of the oil. The mixture of imidazolines obtained by any of the two alternative processes, have high performance characteristics as corrosion inhibitors, low toxicity and good biodegradability.

BEST METHOD FOR CARRYING OUT THE INVENTION The examples presented below show the steps for the preparation of mixtures of imidazolines for processes A and B respectively described in the specification of the invention.

Process A.

STAGE 1 Extraction of coffee waste. 1 Kg of coffee waste with 60% humidity was charged in a 5 L 3-neck flask, 1 L of methanol and 1.4 L of heptane were added and it was heated to reflux with mechanical stirring of 489 rpm for 2 h. It was cooled to 35-40 ° C and filtered, phases were separated and the methanolic phase was returned to the flask along with the solids. The heptane phase was concentrated to dryness with vacuum. 50.53 g of oil and 900 mL of heptane were obtained. 1 L heptane was charged to the flask and heated to reflux for 1 h; it was cooled to 25 ° C, filtered and the phases were separated. The heptane phase was concentrated to dryness, obtaining an additional 8.63 g of oil. The oil from the extracted coffee waste was subjected to a subsequent process for the production of coffee biodiesel.

STAGE 2 Coffee biodiesel. 12. 3 g of coffee oil were heated at 50 ° C for 10 min, a 0.65 M solution of KOH / eOH (184 mg in 5 ml) was added and it was heated in an oil bath at 80 ° C for 1 h. It was verified by TLC (heptane-MTBE 9: 1, iodine developer) complete transformation. It was cooled to 25 ° C and 130 pl of AcOH was added, verifying pH 7. 4 ml of MTBE and 6 ml of brine were added, stirred and the phases were separated. The organic phase was dried over sodium sulfate and concentrated to recover MTBE and 10.2 g of coffee biodiesel, which was further processed for the preparation of mixtures of glycerol-free imidazolines.

STAGE 3 Preparation of glycerol-free imidazolines.

Into a 25 mL flask was charged 10 g of coffee biodiesel and 3.42 g of Huntsman aminoethylethanolamine, heated in an oil bath at 140 ° C with vacuum of 43 Kpa (322.5 mmHg) for 4 h and 1 h at 16-20 mmHg. . It was verified by TLC (heptane-MTBE 9: 1), observing complete biodiesel transformation (revealing with iodine) and by TLC (DCM-MeOH-NH40H 7: 3 + 100 mL / mL), observing complete identity with the ACN- 265 revealing UV and iodine. 12.12 g of the crude mixture of imidazolines were obtained.

Process B.

STAGE 1 Extraction of coffee waste. 1 Kg of coffee waste with 60% humidity was charged in a 5 L 3-neck flask, 1 L of methanol and 1.4 L of heptane were added and it was heated to reflux with mechanical stirring of 489 rpm for 2 h. It was cooled to 25 ° C and filtered, phases were separated and the methanolic phase was returned to the flask along with the solids. The heptane phase was concentrated to dryness with vacuum. 50.53 g of oil and 900 mL of heptane were obtained. 1 L heptane was charged to the flask and heated to reflux for 1 h; it was cooled to 25 ° C, filtered and the phases were separated. The heptane phase was concentrated to dryness, obtaining an additional 8.63 g of oil. The oil from the extracted coffee waste was subjected to a subsequent process for the production of coffee biodiesel.

STAGE 2.

Direct preparation of Imidazolines with glycerol.

In a 25 mL flask, 5 g of coffee oil and 1636 g of AEEA were charged and heated between 140-145 ° C for 1 h at atmospheric pressure and 4 h with a vacuum of 322 mm Hg. TLC was verified by CCF (heptane-MTBE 85:15) complete disappearance of the triglycerides present in the oil and by TLC (DCM-MeOH 7: 3 + 100 mL / mL of NH40H) a stain with strong UV absorption, obtaining 5.3 g of a semisolid brown mass. The mixtures of imidazolines obtained from this process are characterized by containing natural glycerol used as co-solvent.

CLIMBING AT THE PILOT PLANT LEVEL In a 100-gallon (R-1) glass reactor, 52.5 kg of wet coffee bagasse (53.14% w / w moisture), 66.33 kg of methanol and 107.45 kg of n-heptane were charged. It was heated to reflux with stirring at 120 rpm for 2 hours and cooled to 35-40 ° C. It was filtered over a Nutsche filter and the biphasic filtrate was transferred to a separating tank (T-1) to decant the lower methanol-water phase to the R-1 reactor together with the filtered bagasse cake. The R-1 was charged with 107.45 Kg of new n-heptane. The upper phase, containing the oil extract, was transferred to a 100 gallon stainless steel reactor (R-2). The R-1 was heated containing the filtered coffee bagasse and the aqueous-methanolic phase with 107.45 Kg of n-heptane for 2 hours at reflux, after this time, it was cooled between 35-40 ° C. It was filtered again through a Nutsche filter, transferring the oil extract to a separating tank (T-1); the aqueous-methanolic phase was transferred to a 50-gallon reactor for the recovery of methanol; the residue was sent to the treatment plant for disposal and the upper phase was mixed in the R-2 with the first extract. It was concentrated under reduced pressure of 200 mmHg to a volume of 50-55 liters and the residue was concentrated in a 50 L rotavapor until complete elimination of the solvent, obtaining 3.93 Kg of pure coffee oil (16% dry base).

CORROSION INHIBITION TESTS The effectiveness of the imidazolines mixture of coffee residues produced by the above processes was demonstrated by performing electrochemical corrosion tests of polarization resistance and harmonic analysis. The corrosion tests were made on a 1018 AISI steel immersed in corrosive electrolytes with 3% NaCl, C02 and H2S at saturation. Figures 4A, 4B, 4C, 4D and 4E present the individual graphs for the concentrations of the mixture of imidazolines at 5, 10, 25, 50 and 100 parts per million dissolved in the electrolytes referred to above, where it is established for the axis of the ordinates the speed of corrosion and on the axis of the abscissas the unit of time in minutes. The mixture of imidazolines obtained showed effectiveness to mitigate corrosion less than 0.05 mils per year at said concentrations.

Claims (5)

CLAIMS Having sufficiently described my invention, I consider as a novelty and therefore claim as my exclusive property, what is contained in the following clauses:

1. A process for the preparation of mixtures of imidazolines, by processing the oil extracted from the ground coffee waste, characterized in that the mixture of imidazolines obtained have the following general formula (I), where the substituent R corresponds to the hydrocarbon chain of one of the following fatty acids contained in the coffee oil: linoleic acid in greater proportion, palmitic acid, oleic acid and stearic acid. Said process comprises the following stages: a) Extraction of the oil from the waste ground coffee, through a biphasic water-methanol-heptane or water-heptane extraction, with the corresponding separation of the heptane phase and concentration to dryness at moderately reduced pressure between 100 and 200 mmHg, recovering the heptane for reuse and leaving the oil totally free of volatile components. In its case, most of the methanol is recovered by distillation of the aqueous phase. b) The coffee oil obtained is subjected to a transesterification process catalyzed with KOH, obtaining biodiesel from coffee and glycerol; the glycerol is separated from the mixture through a decanting process in a tank with a bottom valve with a glass peephole. c) The coffee biodiesel obtained is subjected to aminolysis process with aminoethylethanolamine (AEEA), by heating between 140 and 160 ° C and a subsequent heating process at the same temperature and 200 to 300 mmHg until the stoichiometric amount is eliminated of water, to produce the mixture of imidazolines of general formula (I).

A process for the preparation of mixtures of imidazolines, by processing the oil extracted from the ground coffee waste, characterized in that the mixture of imidazolines obtained have the following general formula (I), wherein the substituent R corresponds to the hydrocarbon chain of one of the following fatty acids contained in the coffee oil: linoleic acid in greater proportion, palmitic acid, oleic acid and stearic acid. Said process comprises the following stages: a) Extraction of the oil from the ground coffee waste, through a biphasic water-methanol-heptane or water-heptane extraction, with the corresponding separation of the heptane phase and concentration to dryness at moderately reduced pressure between 100 and 200 mmHg, recovering the heptane for re-use and leaving the oil totally free of volatile components. In its case, most of the methanol is recovered by distillation of the aqueous phase. b) The obtained coffee oil is subjected to aminolysis process with aminoethylethanolamine (AEEA), by heating between 140 and 160 ° C and a subsequent delation by heating to 200 to 300 mmHg at the same temperature until the stoichiometric amount of water is eliminated , to produce the mixture of imidazolines of general formula (I).

3. A mixture of imidazolines obtained by means of the processes of claims 1 and 2, characterized in that they incorporate in their structure the linoleic acid contained in the coffee oil, which is doubly unsaturated, which confers to said imidazolines a superior adherence to the metallic surfaces.

4. A mixture of glycerol free imidazolines obtained by means of the process of claim 1, characterized in that the mixture of imidazolines obtained have the following general formula (I), where the substituent hydrocarbon of any of the following fatty acids contained in coffee oil: linoleic acid in greater proportion, palmitic acid, oleic acid and stearic acid

5. A mixture of imidazolines containing natural glycerol derived from the triglycerides of the oil obtained by means of the process of claim 2, characterized in that the mixture of imidazolines obtained have the following general formula (I), wherein the substituent R corresponds to the hydrocarbon chain of one of the following fatty acids contained in the coffee oil: linoleic acid in greater proportion, palmitic acid, oleic acid and stearic acid. The mixture of imidazolines according to claims 4 and 5, characterized in that the waste ground coffee oil, obtained from step a) of said processes, contains hydrocarbon chains of linoleic acid in percentages between 44 and 46%, hydrocarbon chains of palmitic acid in percentages between 32 and 35%; hydrocarbon chains of oleic acid in percentages of between 9 and 10% and hydrocarbon chains of stearic acid in percentages of between 6 and 7%, among other minor fatty acids. The mixture of imidazolines according to claims 4 and 5, characterized in that they find their application as corrosion inhibitors in the hydrocarbon transport, processing and storage industry. The defatted coffee residue obtained in step a) of the processes of claims 1 and 2, characterized in that it is free of residual caffeine which can be used as fertilizer or compost input. SUMMARY The present invention consists in the biphasic extraction of the waste coffee without previous drying to obtain, after concentration of the hydrocarbon phase, the coffee oil, which is transesterified with methanol catalyzed with KOH to produce the mixtures of glycerol-free methyl esters , also called biodiesel from coffee oil, which is subjected to an aminolysis reaction with aminoethylethanolamine (AEEA) between 140-160 ° C at atmospheric pressure with subsequent dehydration by heating at the same temperature but with reduced pressure of 200-300 mmHg, to perform the separation of the intermediate amides from the corresponding imidazolines. In an alternative process, the coffee oil can be subjected to the same aminolysis process with aminoethylethanolamine (AEEA) between 140-160 ° C at atmospheric pressure with subsequent dehydration by heating at the same temperature but with reduced pressure of 200-300 mmHg , to produce mixtures of imidazolines containing the residual glycerol of the original triglycerides. Mixtures of imidazolines obtained by any of the two alternative processes, presents a high performance as corrosion inhibitors. The mixtures of imidazolines obtained according to the present invention are characterized by containing a high degree of unsaturation in the alkyl chains, which gives them greater adherence to metal surfaces than saturated imidazolines. This mixture of imidazolines constitutes a corrosion inhibitor of high performance, low toxicity and good biodegradability